Mongoose – using Populate on an array of ObjectId

For anyone else coming across this question.. the OP’s code has an error in the schema definition.. it should be:

var conversationSchema = new Schema({
    created: { type: Date, default: Date.now },
    updated: { type: Date, default: Date.now },
    recipients: [{ type: Schema.ObjectId, ref: 'User' }],
    messages: [ conversationMessageSchema ]
});
mongoose.model('Conversation', conversationSchema);